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    SubjectRe: debugfs & vfs file permission issue?
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    On Tue 6 Jan 2009 10:20, Mike Frysinger pondered:
    > On Tue, Jan 6, 2009 at 10:12, Robin Getz wrote:
    > > On Tue 6 Jan 2009 07:05, Robin Getz suggested:
    > >> adding a readonly, and writeonly, and ensuring that when you call
    > >> debugfs_create_*, the mode is checked, and the "correct" fops are set
    > >> doesn't seem like it would be a bad idea? This would enforce the
    > >> kernel programmer's view on the world, and not allow pesky root users
    > >> to override things....
    > >>
    > >> Greg - would you take something like that?
    > >
    > > How about this?
    > >
    > > Feel free to nak it - we can do the same thing where we are calling the
    > > debugfs_create_* functions - this just makes it cleaner in my opinion.
    > >
    > > ---
    > >
    > > In many SOC implementations there are hardware registers can be read only,
    > > or write only. This extends the debugfs to enforce the file permissions for
    > > these types of registers, by providing a set of fops which are read only
    > > or write only. This assumes that the kernel developer knows more about the
    > > hardware than the user (even root users) - which is normally true.
    >
    > we want it for cpu registers, but i dont see any reason why this
    > wouldnt also apply to external devices attached via memory interfaces
    > ... fifos and such ...

    Yes - Although the existing use case is for SOC on chip registers - it applies
    to anything where the kernel developer really doesn't want to allow the
    user to do an access that will cause a negative side effect (crash, effect
    fifos, etc).

    -Robin


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